The invention is related to a transmission system comprising a transmitter for transmitting digital symbols via a transmission channel to a receiver, said receiver comprises a detector, said detector comprising quality measure determining means for determining a quality measure of the input signal, the detector being arranged for deriving a sequence of reconstructed symbols from the input signal and the quality measure.
The invention is also related to a receiver, a recording system, a detector and a detection method.
A transmission system according to the preamble is known from the published international patent application WO 96/13905.
Such transmission systems find its use, for example, for transmitting digital symbols through the public telephone network, for transmitting multiplex signals between telephone exchanges or for transmitting digital signals in mobile telephony systems. Said recording systems may be used for recording and reproducing digital symbols using magnetic tape or magnetic discs such as hard discs and floppy discs. Such recording systems may also be used with optical or opto-magnetic discs, such as CD, CD-ROM or DVD (Digital Video Disc).
For transmitting source symbols via a transmission channel, or recording source symbols on a recording medium, these source symbols are often converted into coded symbols. A possible object of coding is obtaining a signal representing a sequence of coded symbols which has a frequency spectrum which meets specific requirements. One of these requirements is, for example, the lack of a DC-component, because a number of frequently used transmitting channels or recording media are incapable of transmitting a DC component. Another reason for the use of coding is obtaining the possibility of correcting transmission errors.
In the known transmission system a detector is used which makes decisions about the symbol value symbol-by-symbol. In order to increase the reliability of the detector, this detector comprises error detection means which detects transmission errors. The detector also comprises error correction means for correcting the value of the least reliable symbol(s) on basis of a quality measure associated with the detected symbols. In the known transmission system this quality measure is derived from the analog signal value at the instant on which the decision about the symbol value is taken. The use of the analog signal value for determining the quality measure requires additional hardware for determining and storing said analog signal value.
The object of the present invention is to provide a transmission system according to the preamble which does not require the above mentioned additional hardware.